With the increasing concern for safety, there is a positive move toward providing safe materials for public and household use. One particular area of need is that of providing flame retardant, non melt-drip and non-opaque products having good abrasion, mar, and chemical resistance for use by the ultimate consumer. As a result of this demand, many products are being required to meet certain flame retardant criteria both by local and federal government and the manufacturers of such products. One particular set of conditions employed as a measuring standard for flame retardancy is set forth in Underwriters' Laboratories, Inc. Bulletin 94. This Bulletin sets forth certain conditions by which materials are rated for flame retardant characteristics.
In the art, there are many known flame retardant additives which are employed by mixing with products to render such materials flame retardant. Such flame retardant additives have been known to be employed in amounts of 5 to 20 weight percent in order to be effective in avoiding burning of those products which are combustible. It has also been found, however, that such amounts can have a degrading effect upon the base product to be rendered flame retardant, resulting in the losses of valuable physical properties of the base product. This is particularly so when employing known flame retardant additives with the base product polycarbonate resins. Many of these known additives have a degrading effect upon the polymer.
Furthermore, in many instances, it is desirable that articles produced from these first retardant polycarbonate resins not only be fire retardant but that they also be non melt-dripping, i.e., not melt-drip upon the application of flame and/or heat thereto, and resistant to abrasion, marring, and chemical attack, while at the same time retaining their non-opaque characteristics.
While commercial liquid coating compositions are available, many of the coating compositions are not suitable for coating polycarbonate articles since they are not compatible with the polycarbonate. Also, the uncured coating may adversely affect the polycarbonate article by stress cracking and crazing it, by causing crack propagation into the polycarbonate as a result of brittleness of the coating itself and/or by reducing the properties of the polymer generally such as, for example, impact resistance, elongation, tensile strength and so on. Further, several coatings, while compatible with the polycarbonate, have little or no chemical barrier properties and/or poor adhesion while others impart little or no non-drip properties to the polycarbonate.
Therefore, a successful non-drip coating for polycarbonate articles must be compatible with the polycarbonate, provide barrier or other desirable surface properties while maintaining mechanical or other properties of the polymer substrate and themselves provide chemically resistant surfaces, and be drip-resistant when exposed to flames and/or heat.